The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, a hybrid vehicle is a future type vehicle that is driven via a combination of an engine and a motor and is classified into a parallel-type car, a serial-type car, a combination-type car, and so on, according to a driving method. A hybrid vehicle may also be classified into a mild-type car, a middle-type car, and a hard-type car according to a power division ratio of the engine and the driving motor. The hard-type car has a driving motor with high capacity compared with an engine, the mild-type car has a driving motor with low capacity compared with an engine, and the present disclosure relates to a mild hybrid system.
In particular, a mild hybrid system refers to a system that does not have a driving mode in which a vehicle is driven by a driving motor only but supplies torque desired for driving using a hybrid starter generator (HSG) with fast response compared with an engine in order to instantly gain high torque during acceleration in a stop state of a vehicle or outstrip acceleration in a driving state.
In this regard, Korean Patent No. 10-1592828 (Control Method of Hybrid Vehicle) discloses a control method of a hybrid vehicle at the time of starting by an HSG only and, in detail, a control method of a hybrid vehicle in which a driving motor is connected between an engine and a transmission, the engine and the driving motor are connected through an engine clutch, and an HSG is connected to the engine.
However, the cited reference discloses a technology for determining a battery SOC state and, thus, when an engine is driven under a starting condition of a 48 V HSG, there is a limit in terms of Mild Hybrid Starter Generator (hereinafter termed “MHSG”) efficiency and belt slip